Elm Court, also known as Phillips Mansion, is a house located off E. Elm Street in Butler. The home is owned by Fredrick Koch, who's brother David Koch died Friday at the age of 79.

WASHINGTON — Billionaire industrialist David H. Koch, who with his older brother Charles was both celebrated and demonized for transforming American politics by pouring their riches into conservative causes, died Friday at 79.

The cause of death was not disclosed, but Koch Industries said Koch, who lived in New York City, had contended for years with various illnesses, including prostate cancer.

A chemical engineer by training, Koch was an executive in the family-run conglomerate, the Libertarian Party’s vice-presidential candidate in 1980 and a major benefactor of educational, medical and cultural organizations. But he and his brother became best known for building a political network dubbed the “Kochtopus” for its many-tentacled support of conservative and libertarian causes and candidates.

“I was taught from a young age that involvement in the public discourse is a civic duty,” David Koch wrote in a 2012 op-ed in the New York Post. “Each of us has a right — indeed, a responsibility, at times — to make his or her views known to the larger community in order to better form it as a whole. While we may not always get what we want, the exchange of ideas betters the nation in the process.”

While lionized on the right, the Koch brothers have been vilified by Democrats who see them as a dark and conspiratorial force, the embodiment of fat-cat capitalism and the corrupting influence of corporate money in American politics.

David Koch had stepped away from a leadership role in recent years because of declining health, including a decades-long battle with prostate cancer, and his brother became the network’s public face.

In an interview after the 2012 Republican convention, his mind was on his legacy.

Koch donated $100 million in 2007 to create a cancer research institute at the Massachusetts Institute of Technology. He also gave millions to Johns Hopkins University in Baltimore, the Memorial Sloan-Kettering Cancer Center in New York, the M.D. Anderson Cancer in Houston and other institutions.

He said his philanthropy was fueled by a brush with death during a 1991 collision of two airliners at the Los Angeles airport.

Charles and David Koch, each with an estimated net worth of $50.5 billion, were tied for 11th place in 2019 on the Forbes 500 list of the nation’s richest men. Koch Industries, co-founded by their father, Fred, in 1940, is a Wichita, Kansas-based conglomerate with vast holdings in oil refineries, paper mills, fertilizer plants, cattle ranches and other ventures. It is the company behind Stainmaster carpeting, Brawny paper towels and Dixie cups.

It has drawn fire for years from environmental advocates and researchers. Koch Industries in 2000 paid $35 million — then the largest civil fine ever levied under the federal Clean Water Act — to settle lawsuits over oil pipeline leaks into lakes and streams in six states.

David Koch, who held degrees from MIT, served on Koch Industries’ board and was also CEO of a Koch chemical subsidiary. He retired from the company as executive vice president in 2018.

Two other Koch brothers, Frederick and Bill Koch, came out on the losing end of a power struggle for control of the company’s board. They sold their stake in Koch Industries in 1983, later unsuccessfully claiming in a lawsuit that they were cheated out of more than $1 billion. David and Bill Koch were twins.

Frederick Koch, one of David Koch’s brothers, is listed on Butler County property records as the owner of a large historic mansion in the city of Butler commonly known as Elm Court or the Phillips mansion.